mSubscription.unsubscribe onCreate在活动中的作用与onDestroy相同吗

Question

1. rxjava mSubscription.unsubscribe onCreate在活动中的工作方式与onDestroy相同吗？

2. 它会以同样的方式工作吗？通过将其作为subscription.subscribeOn().observeOn().subscribe().unsubscribe放置在onCreate中来取消订阅以防止内存泄漏因为"活动"不断被调用以填充下一个片段并弹回堆栈。如果mSubscription.unsubscribe是在"活动"的onDestroy中完成的，则会给出RunTimeException：由于NullPointerException 而无法销毁活动

3. 我是不是错过了一些生命周期问题？

谢谢！

private ViewPager viewPager;
private TabLayout tabLayout;
private int mPosition;
private String id;
private Subscription mSubscription;
private Context mContext;
private RealmResults<Experience> realmResults; 
private String animateExtraColumnName, tag;
private Boolean automaticUpdate, animateResults;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_employment);
User currentUser = AppDelegate.getCurrentUser();
assert currentUser != null;
mEmployee = getRealm().where(Employee.class).equalTo("user.id", currentUser.getId()).findFirst();

//Server returns Experience's ID
if (employeeExperience == null) {
AccessToken accessToken = currentUser.getAccessTokenAsTokenType(AppDelegate.getContext(), "Bearer");
employeeExperienceAPIOAuth2Call apiCall = new employeeExperienceAPIOAuth2Call(AppDelegate.getContext(), accessToken);
Observable<ResponseEmployeeExperience> postEmployeeExperienceObservable = apiCall.postEmployeeExperiencesRX();
mSubscription = postEmployeeExperienceObservable
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe((data) -> {
Log.d(TAG, "onCreate: Subscribe ");
employeeExperience = data.getEmployeeExperience();
Log.d(TAG, "onCreate: employeeExperience.getId()");
getRealm().beginTransaction();
getRealm().copyToRealmOrUpdate(employeeExperience);
// This adds the new employeeExperience object into the EmployeeExperiences RealmList
employee.employeeExperiences.add(employeeExperience);
getRealm().commitTransaction();
getRealm().close();
//unsubscribe here because the activity doesnt close itself to begin with?
mSubscription.unsubscribe();
Log.d(TAG, "onCreate: Unsubscribe: ");
// prepare data needed by our fragment
FragmentAddOrUpdateEmploymentHistory addEmploymentHistoryFragment = new FragmentAddOrUpdateEmploymentHistory();
FragmentManager fm = getSupportFragmentManager();
fm.beginTransaction().replace(R.id.edit_frame_layout, addEmploymentHistoryFragment, "EDIT_FRAGMENT").commit();
}, (error) -> {
// TODO do whatever error handling we need to do here
Log.d(TAG, "onCreate: postEmployeeExp error");
error.printStackTrace();
});
}
} else if (employee.getEmployeeExperiences() != null) {
employeeExperience = getRealm().where(employeeExperience.class).equalTo("id", id).findFirst();
FragmentAddOrUpdateEmploymentHistory addEmploymentHistoryFragment = new FragmentAddOrUpdateEmploymentHistory();
FragmentManager fm = getSupportFragmentManager();
fm.beginTransaction().replace(R.id.edit_frame_layout, addEmploymentHistoryFragment, "EDIT_FRAGMENT").commit();
}
ImageButton checkButton = (ImageButton) findViewById(R.id.edit_toolbar_check);
checkButton.setOnClickListener(this);
ImageButton crossButton = (ImageButton) findViewById(R.id.edit_toolbar_cross);
crossButton.setOnClickListener(this);
}
@Override
protected void onStart() {
super.onStart();
}
@Override
public void onClick(View view) {
Fragment editFragments = getSupportFragmentManager().findFragmentByTag("EDIT_FRAGMENT");
switch (view.getId()) {
case R.id.edit_toolbar_check:
if (editFragments instanceof FragmentEditDate) {
Log.d(TAG, "onClick: editdate ");
getSupportFragmentManager().popBackStack();
} else if (editFragments instanceof FragmentSalary){
Log.d(TAG, "onClick: salary ");
getSupportFragmentManager().popBackStack();
} else if (editFragments instanceof FragmentAddOrUpdateEmploymentHistory) {
Log.d(TAG, "onClick: employmenthistory ");
finish();
} else if (editFragments instanceof FragmentSingleChoice) {
Log.d(TAG, "singlechoice  " );
getSupportFragmentManager().popBackStack();
}
else if (editFragments instanceof FragmentMultipleChoice) {
Log.d(TAG, "multiplechoice  " );
getSupportFragmentManager().popBackStack();
}
break;

case R.id.edit_toolbar_cross:
if (editFragments instanceof FragmentAddOrUpdateEmploymentHistory) {
getRealm().beginTransaction();
employeeExperience.DELETE();
getRealm().commitTransaction();
getRealm().close();
}
finish();
} else {
finish();
}
} else {
getSupportFragmentManager().popBackStack(); }
break;
}
}

Answer 1

简而言之，一旦订阅了Observable，就可以接收来自它的通知并对其做出反应(onNext、onError、onComplete)。此外，在大多数情况下(对于冷Observables)，这实际上是Observable开始发射项目的触发点。

来自Observable的Unsubscribing意味着您不再有兴趣接收任何进一步的通知。当您不再希望接收任何内容时，您需要unsubscribe，类似于在"活动"的onDestroy()方法中释放任何资源的方式。当然，与活动生命周期的并行只是为了进行比较——订阅/取消订阅过程是完全独立的。

您可以详细阅读subscribing和unsubscribing的含义[此处][1][1]：http://reactivex.io/documentation/contract.html

也就是说，对你的代码很少有具体的建议：

你目前在安卓的主线程上执行的内容太多了。我建议将所有真正相关的东西作为RX链的一部分移动，而不是在subscribe(...)中的onNext()处理程序中移动。通过这种方式，它将在io线程上执行。类似于：

...
mSubscription = postEmployeeExperienceObservable
.subscribeOn(Schedulers.io())
.doOnNext(data -> saveDataToRealm(data))
.observeOn(AndroidSchedulers.mainThread())
.subscribe((data) -> {
// prepare data needed by our fragment
FragmentAddOrUpdateEmploymentHistory addEmploymentHistoryFragment = new FragmentAddOrUpdateEmploymentHistory();
FragmentManager fm = getSupportFragmentManager();
fm.beginTransaction().replace(R.id.edit_frame_layout, addEmploymentHistoryFragment, "EDIT_FRAGMENT").commit();
}, (error) -> {
// TODO do whatever error handling we need to do here
Log.d(TAG, "onCreate: postEmployeeExp error");
error.printStackTrace();
});
}
private Data saveDataToRealm(Data data) {
employeeExperience = data.getEmployeeExperience();
Log.d(TAG, "onCreate: employeeExperience.getId()");
getRealm().beginTransaction();
getRealm().copyToRealmOrUpdate(employeeExperience);
// This adds the new employeeExperience object into the EmployeeExperiences RealmList
employee.employeeExperiences.add(employeeExperience);
getRealm().commitTransaction();
getRealm().close();
}

就取消订阅而言——如果你真的想从onNext()事件中订阅unsubscribe，更好的策略是通过Subscriber<Data>订阅，然后只使用它的unsubscribe()方法。换句话说，您不会调用mSubscription.unsubscribe()，而是调用this.unsubscribe()。

mSubscription = postEmployeeExperienceObservable
.subscribeOn(Schedulers.io())
.doOnNext(data -> saveDataToRealm(data))
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Subscriber<Data>() {
@Override
public void onCompleted() {
}
@Override
public void onError(Throwable e) {
}
@Override
public void onNext(Data data) {
...
this.unsubscribe();
}
});

话虽如此，我认为在您的情况下，您真的不需要从onNext()方法中unsubscribe，相反，您可以在onDestroy()中这样做，当然，检查之前是否创建了订阅：

@Override
protected void onDestroy() {
super.onDestroy();
if (mSubscription != null) {
mSubscription.unsubscribe();
}
}